Single high-frequency interaction gap klystron with means for increasing the characteristic impedance



July 21, 1970 VF. POTZL 3,521,116

SINGLE HIGH-FREQUENCY INTERACTION GAP KLYSTRON WITH MEANS FOR INCREASING THE CHARACTERISTIC IMPEDANCE Filed Jan. 30. 1968 2 Sheets-Sheet 1 Fig] FigZ .INVENTOR. v FRIEDRICH POTZL BY v N I Ami July 21, 1970 F. POTZL 3,521,116

SINGLE HIGHFREQUENCY INTERACTION GAP KLYSihC/N wzm MEANS FOR INCREASING THE GHARACTERISTIC IMPEDANCE Filed Jan. 30. 1968 2 Sheets-Sheet 4 INVENTOR. FRIEDRICH POTZL United States Patent US. Cl. 3155 8 Claims ABSTRACT OF THE DISCLOSURE Single high-frequency interaction gap klystron formed by an inner evacuated cavity at least partially surrounded by an outer chamber with drift tubes which extend into the inner cavity and define a gap therebetween. Means are provided in the cavity for increasing the characteristic impedance which substantially exclusively store magnetic energy and increase induction without substantially contributing to the capacitance of the cavity electrodes.

The invention relates to a klystron comprising a composite electromagnetic cavity, which cavity comprises an exhausted inner chamber bounded by two rotation-symmetrical metal flanges and a tube of insulating material provided therebetween. The inner chamber is surrounded at least partially by at least one outer chamber which is not evacuated. The outer chamber has a conductive outer wall. A single HF-interaction gap is provided in the inner chamber between drift tubes terminating therein, the axial length of said interaction gap being smaller than a quarter of the wave length of the operative wave.

It must be understood that the inner chamber and the outer chamber(s) surrouding it, which are mechanically separated, are to be considered in electrical respect as a single klystron cavity, which is the said composite electromagnetic cavity.

There are known klystrons of this type which are suitable for use in television band IV. For this UHF-range the required klystron cavity portions are relatively small and convenient to handle so that the structure of transmitting tubes does not cause special difficulties.

In the demand for development of klystrons of the type described in the first paragraph which must be suitable for use at comparatively low frequencies, such as in the television band III (174 mc./s.223 mc./s.) the difficulty is encountered that such a klystron built up from conventional parts cannot have convenient dimensions and at the same time present a satisfactory bandwidth accompanied by permissible losses due to radiation. The difficulties actually reside in the fact that a high characteristic resistance is required which is difficult to realize. Said resistance is given by the relation Q Q a C C For a resonance resistance R=12K9 and a 3 db bandwidth of approximately 4 mc./s. said characteristic resistance is approximately 2159 for 223 mc./s. and approximately 1760 for 174 mc./s. Thus klystron cavity portions of extremely large dimensions, for example, 1 x 1 /2 sq. in. would be required in klystrons including conventional oscillatory circuits which are suitable for television band III. The use of concentrated structural elements, for example, a coil which is directly connected to the klystron flanges has the the additional drawback of specially strong radiation. A reduction of the required dimensions by folding the conduction circuit or by additiona1 capacitive loads exceeding the tube capacitance has the drawback of reducing the bandwidth. Building up the oscillatory circuit of the tube capacitance and aconcentrated inductive element, for example, a coil has the drawback that a sufliciently contiguous screen will be substantially short-circuiting the element.

An object of the invention is to find a solution for the said problems and to provide a klystron for low frequencies such as television band III which satisfies the combination of practical requirements of convenient dimensions, sufiicient bandwidth and small dispersion.

According to the invention, in a klystron of the kind as specified in the first paragraph, means for increasing the characteristic impedance are provided in the cavity, which means almost exclusively store magnetic energy and increase the induction and substantially do not contribute to the capacitance of the cavity electrodes. If the coaxial E-field configuration may just commence to blend with the radial wave a maximum bandwidth can be obtained. A maximum wave impedance before the transition into a radial guide which becomes more low-ohmic with increasing external diameter can be obtained in this manner.

The said means may be designed in various advantageous manners. In a simple embodiment of the klystron a ring the outer periphery of which narrows in the axial direction is provided opposite the termination of a drift tube in the inner chamber as an internal induction-raising means increasing the induction within the inner chamber. The ring may be supported by bars. Such an embodiment is very simple in structural respect and provides the possibility of a very satisfactory screening of the inner chamber. The ring is preferably supported by at least one helical current conductor, which preferably forms half a turn about the axis of the inner chamber. With a view to special requirements, for example, concerning the bandwidth the pitch of the helical conductor may be chosen advantageously.

In a further embodiment, an internal means increasing the induction is formed by an end of a drift tube extending into the inner chamber and surrounded by discs, the outer periphery of said end narrowing in the axial direction. The discs load substantially the drift paths thus causing increasing of induction and permitting in addition an effective cooling. The discs may have equal constant outer peripheries. The means increasing the induction can also be formed by at least one helical current conductor provided between the klystron flanges within or directly around the inner chamber, and at least one end of said current conductor is connected to a klystron flange. The axis of the turns may then, for example, coincide with the axis of the inner chamber. In that case the conductor may be provided within the inner chamber. This is preferred if the klystron is intended for use at fixed frequencies, when no frequency variation is required after manufacture. The current conductor may, however, also surround the inner chamber. The conventional screenings starting from the separate klystron flanges remain usable if only one end of the current conductor is secured to a klystron flange, the other end remaining free. The axis of the turns can alternatively be perpendicular to the axis of the inner chamber. It is true that in that case more dispersion losses occur than in the embodiments described hereinbefore, but actually fewer losses than with devices including klystrons of the known kind. In special embodiments the ends of a plurality of helical conductors are secured to adjusting members which are movably arranged on the klystron flanges. This has the advantage that the pitch of the turns and the section of the turns remains adjustable for frequency variation.

It is alternatively possible to arrange spiral-shaped slots in the outer wall of the outer chamber as a means increasing the induction. Said slots provide a means of very little dispersion.

The invention may be readily carried into eifect, it will now be described in detail, with reference to the accompanying drawing in which:

FIG. 1 shows one embodiment of an inner chamber including internal means increasing the induction for a klystron according to the invention.

FIG. 2 shows a further embodiment of such a chamber.

FIG. 3 shows a third embodiment of such a chamber.

FIG. 4 shows one embodiment of an inner chamber provided with external means increasing the induction for a klystron according to the invention.

FIG. 5 shows a further embodiment of such a chamber.

FIG. 6 shows a third embodiment of such a chamber.

FIG. 7 shows part of an outer wall containing means increasing the induction of an outer chamber of a klystron according to the invention.

In FIG. 1 the exhausted inner chamber is indicated by 1. The chamber 1 is bounded by rotation-symmetrical metal flanges 2 and 3 and a tube 4 of insulating material provided therebetween. Drift tubes 5 and 6 terminate in the cavity 1. The means increasing the induction are rings 7 and 8 supported by bars 9, and bevelled at their outer peripheries.

In FIG. 2 the rings 7 and 8 are supported by helical current conductors 10 each forming half a turn the axis of which coincides with the axis 11 of the chamber 1.

In FIG. 3, ends 12 and 13 of the drift tubes 5 and 6 extend into the chamber 1. The ends 12 and 13 have outer peripheries narrowing in the axial direction to which discs 15 of a constant outer periphery are secured. As is shown in the lower portion of the figure, the discs may be welded to extensions 16. The discs 15 form slots 17 thus resulting in a delay structure.

In FIG. 4 the flanges 2 and 3 are externally provided with a screen 18 which may also be present in the embodiments of FIGS. 1, 2 and 3. The ends 12 and 13 of the drift tubes again extend into the inner chamber 1 bounded by the flanges 2 and 3 and the tube 4. The exhausted cavity is surrounded by unexhausted outer chambers 19 and 20 which may be considered as one chamber in electrical respect. The current conductor 21 surrounds the tube 4, the conductor having 1 /2 turns about the axis of the inner chamber. One end of the current conductor is secured to the klystron flange 2, while the other end hangs loose. The current conductor 21 can also be provided within the inner chamber. For this reason the tube 4 bounding the inner chamber is shown by broken lines in FIG. 4.

In the embodiment of FIG. 5, a plurality of current conductors 22 surround the tube 4 bounding the inner chamber. The current conductors 22 are secured to an of two wall portions separated at 26 which can be pushed from aside onto the rotation-symmetrical inner chamber. The bore 27 then accommodates a klystron flange. The increasing of induction is obtained due to slots extending outwards in the form of spirals, beginning at a certain distance from the bore.

What is claimed is:

1. A klystron comprising a composite electromagetic cavity, said cavity comprising an evacuated inner chamber bounded by two rotation-symmetrical metal flanges and a tube of insulating material provided therebetween, said inner chamber being surrounded at least partially by at least one outer chamber which is not evacuated, said outer chamber having a conductive outer wall, a single In -interaction gap being constituted in said inner chamber between drift tubes terminating therein, the axial length of said interaction gap being smaller than a quarter of the wave length of the operative .wave, and means for increasing the characteristic impedance in said cavity, said means substantially exclusively storing magnetic energy and increasing the induction and substantially not contributing to the capacitance of the cavity electrodes.

2. A klystron as claimed in claim 1, wherein a ring the outer periphery of which narrows in the axial direction is provided within said inner chamber opposite the termination of a drift tube.

3. A klystron as claimed in claim 2, wherein the ring is supported by at least one helical current conductor.

4. A klystron as claimed in claim 3 wherein the helical current conductor forms half a turn about the axis of the inner chamber.

5. A klystron as claimed in claim 1 wherein one end of a drift tube extends into the inner chamber the outer periphery of said end narrowing in the axial direction toward the interaction gap and being surrounded by at least two axially consecutive discs fastened to said narrowing outer periphery.

6. A klystron as claimed in claim 1 wherein at least one helical current conductor is provided between the klystron flanges [within or directly around the inner chamber, at least one end of said conductor being connected to a klystron flange.

7. A klystron as claimed in claim 6, wherein the ends of a plurality of helical conductors are secured to adjusting members which are movably arranged on the klystron flanges.

8. A klystron as claimed in claim 1, wherein said outer wall of said outer chamber is provided with spiralshaped slots.

References Cited UNITED STATES PATENTS 2,405,611 8/1946 Samuel 3 15-5 .41 X 2,647,219 7/ 19'53 Touraton et al. 315-5.39 X 3,104,340 9/ 1963 Crapuchettes et al. 3155.39 3,316,440 4/1967 Le Boutet et al. 3155.42 X 3,390,301 6/ 196 8. Sawada et al. 315-5.'39

ELI LEIBERMAN, Primary Examiner S. CHATMON, JR., Assistant Examiner U.S. Cl. X.R. 

